Tropical and subtropical shrubs and trees of the Combretaceae family represent a practically unexplored reservoir of new substances with potentially useful biological properties. Illustrative is the genus Combretum with 25 species (10% of the total) known in the primitive medical practices of Africa and India for uses as diverse as treating leprosy (See: Watt, J. M. et al, "The Medicinal and Poisonous Plants of Southern and Eastern Africa", E. & S. Livingstone, Ltd., London, 1962, p. 194) (Combretum sp. root) and cancer (Combretum latifolium). But only a few species principally Combretum micranthum (used in northern Zimbabwe for mental illness) (See: Ogan, A. U., Planta Medica, 1972, 21, 210; and Malcolm, S. A. et al, Lloydia, 1969, 32, 512.) and C. zeyheri (for scorpion invenomation) (See: Mwauluka, K. et al, Biochem. Physiol. Pflanzen, 1975, 168, 15) have received any scientific study.
The present investigation was undertaken to determine the murine P388 lymphocytic leukemia (PS system) inhibitory constituents of Combretum caffrum (Eckl. and Zeyh) Kuntze (also as C. salicifolium E. Mey), a potentially useful lead which came out of the U.S. National Cancer Institute's world-wide exploratory survey of plants. In South Africa this tree is known by the Zulu as Mdubu (used as a charm) and is otherwise known as bushveld willow, bushwillow and rooiblaar. The timber is principally used on African farms as scrap wood and fuel. Interestingly, honey arising from the nectar of this tree is strongly bitter but no problems have been recorded from human consumption.